This invention originated from the pioneering effort of the inventor in the development of laser radar since 1963 starting at the Royal Radar Establishment in Malver, U.K. Laser radar is particularly attractive for ranging to targets which are in environments which themselves provide radar reflections if the beamwidth of the said radar is too large. For example, low flying aircraft are difficult to detect with microwave radar whose beamwidth not only covers the target but also the ground over which it flies. On the other hand, very narrow beamwidth laser radar can emit a laser beam whose width is so narrow that only a small portion of said target intercepts said beam so that no ground clutter results and the detected signal to noise ratio is very large. Having perfected the technique of pinpointing the range of the low flying target, one needs more information to identify said target and this can only be achieved effectively by either broadening the said laser beamwidth to illuminate the whole target or by scanning the narrow beamwidth across the whole target. Once the techniques to scan such narrow beamwidth laser beams in two dimensions were mastered, it became possible to scan the said targets in three dimensions. Hughes 1980 (U.S. patent classified).
The commercial spin-offs of this defence technology is obvious in many areas but in particular in the recording and projection of three dimensional static and moving images (Hughes, co-pending patents). In these processes, the three dimensional image is built up laser spot by laser spot within a scattering medium. For example, if it needs one hundred spots to define one edge of a cube, it will need one million such spots to project a cube of one centimeter per side. To avoid flicker to the observer, such a cube image would have to be projected at thirty frames per second implying the generation of thirty million spots per second is needed to generate a flicker free, three dimensional image of a cubic centimeter in volume.
However, if such an image was projected inside a medium such as liquid plastic using an ultra-violet laser beam, then a hard-copy, three dimensional model of said image would result. Similarly, if such a laser beam imaging technique was used to sculpture a solid object, a three dimensional hard copy of the image would result.
Applying laser radar three dimensional laser beam target imaging techniques to the polymerisation of liquid plastics we establish an avenue involving the use of computer controlled laser beam image profiling or in other words dynamic beam image profiling. However, the fact that the phased-array lasers used in advanced laser radar systems, which have output apertures consisting of a large number of individual laser beam transmitters, are capable of emitting their output beams in the form of high quality, real time images simply by the selective switching of the individual transmitters (Hughes U.S. Pat. No. 4,682,335 issued July 1987) which allows an appropriate real time image stencil to be impressed onto a laser beam at the high power levels necessary for liquid plastic polymerisation. A similar result can be achieved using liquid crystal light valve based laser beam imaging systems (Hughes. U.S. Pat. No. 4,586,053 issued Apr. 29th, 1986) which allows an appropriate real time image stencil to be impressed onto a laser beam at low power levels and amplified to the higher power levels necessary for liquid plastic polymerisation. These static beam imaging techniques will be referred to as static beam image profiling.
In the dynamic beam mode, it is advantageous to project the focussed laser beam into the liquid plastic tank as near as possible to the normal to the entrance window in order to avoid parallax effects which occur from non-normal incidences. This gives rise to a range of laser beam manipulation techniques depending on whether or not each laser beam is deflected by one or more mirrors. Once set for normal incidence across the window surface, the incidence laser beam can be deflected in a precise, computer controlled manner around normal incidence, the laser beam scanner described by Hughes (U.S. Pat. No. 4,209,253 issued June 1980) is effective. In this way, the relatively slow mutually orthoganal movement of the incident laser beam over the whole aperture of the tank window is adequately compensated for by very rapid polymerisation product profiling within the liquid plastic tank around the region of the laser beam normal incidence at any given point on the aperture of the entrance window into said tank.
A high quality, focussed laser beam image can be projected into the said liquid plastic tank through its entrance window in the form of a real time stencil produced as described by Hughes (U.S. Pat. No. 4,586,053 issued Apr. 29th, 1986). For a given setting of the piston within said liquid plastic tank, the projected laser beam image is set to the appropriate cross-sectional configuration of the three dimensional plastic model to be produced via the imaged ultra-violet laser beam induced plastic polymerisation process within the said tank of liquid plastic. If said images are originally produced at other than ultra-violet wavelengths, they can be frequency shifted into the ultra-violet region by using techniques known in the art.
By combining the dynamic, focussed laser beam polymerisation process in liquid plastic with the static, real time stencil laser beam imaging polarization process in liquid plastic it is possible to generate the fine structure via the high resolution beam imaging plastic polymerisation process with the less accurate, but much more rapid, dynamic laser beam polymerisation process which is used to fill in the areas not demanding the highest resolution in the manufacturing of plastic models, for example the internal body structures.
Phased-array lasers, for example laser diode array, phased-array lasers and fibre bundle based phased-array lasers, emit their outputs from as many as one million minute transmitters per square centimeter of their output aperture. Even in their non-phased-locked format and with appropriate beam collimation, such lasers are capable of emitting their outputs in the form of high resolution images which can then be projected into the liquid plastic tank of the present invention. When coherently phased-locked across their output apertures the output beams of such lasers can be scanned without the use of mirrors, the processes having response times of the fastest electro-optic switches in the art at a particular development period. For example, if an electro-optic switch with a ten nanosecond (10.sup.-8 seconds) response time is available, as has been the case for many years past, then it is possible to scan to output beam of a coherently phased locked, phased-array laser in a period of ten nanoseconds and to repeat this processes one hundred million times per second provided the switching means can stand up to the task. New switching techniques for scanning the output beams of phased-array lasers are being intensely developed worldwide and the situation is likely to rapidly improve which in turn implies that the use of such phased-array lasers in this invention will lead to continual improvement in the production of the laser induced polymerised plastic models.